Hi Alan

I have used cutters from a wide range of different suppliers. Price hikes are all dependant on supplier! There is a company (that I cant recall off the top of my head) that specialise in "micro cutters". They don't go below 0.3mm BN tho.

Getting a 0.4BN into a slot is easy... its the depth of the slot that really makes things difficult! I would say if the slot was deeper than 2.25 times the diameter of the cutter then you should start investigating other methods of manufacture, like EDM.

Hope this helps.